It is proposed to examine the development, distribution, origin and function of different components of antibody and cellular reactivity in human colostrum and milk. The investigations will be undertaken in groups of lactating post partum women immunized subcutaneously or intranasally with RA27/3 or HPV-77 DE/5 live attenuated rubella vaccine and in lactating women with other naturally acquired respiratory viral infections. A variety of currently available virologic and immunologic techniques will be employed. Studies will be undertaken to determine the relative contribution of bronchus associated lymphoid tissue (BALT) to the development of immunocompetence in human breast milk. Other studies will be initiated to delineate the role of breat feeding in the development of immunologic reactivity to viruses in the breat feeding infant and young child, using immunization with rubella virus vaccine as an investigative model. It is also hoped to study other immunologic aspects of maternal neonatal interaction which may be influenced by breast feeding. These studies should have significant relevance to protective mechanisms against viral infection in the developing human neonate.